DES MOINES, Iowa — A federal judge in California has ordered the removal from the ground of plants grown to produce seeds for genetically modified sugar beets, citing the potential for environmental harm.

The ruling by U.S. District Judge Jeffrey White has again raised questions about the use of genetically modified crops and what will happen if growers aren't allowed to plant GMO seeds.

About 95 percent of the sugar beet crop has been genetically modified to resist the weed killer Roundup. The crop provides roughly half of the nation's sugar supply.

White ruled in a lawsuit filed by environmental groups challenging a decision in September by the U.S. Department of Agriculture's Animal and Plant Health Inspection Services to issue permits to seed companies to plant sugar beet stecklings. The young plants produce seeds that then are planted to grow sugar beets.

The agency decided to issue the permits despite an August ruling by White that put a hold on future planting of genetically modified sugar beets. The ruling allowed this year's crop to be harvested and processed, but the current seed crop was not to be planted until the USDA reviewed the effects the crops could have on other food.

In his order Tuesday, White wrote that the environmental groups had shown that the genetically modified sugar beets could contaminate other crops, including through cross-pollination.

"The likely environmental harm . . . is irreparable," White wrote.

The plants in question would produce seeds for crops to be planted in the spring of 2012. Crops that will be planted next spring won't be affected by the decision.

Analysts have said an inability to plant genetically altered sugar beets would likely force a big jump in sugar imports and increased prices.

The defendants in the case filed a request for an emergency stay of White's ruling, saying that without it, the sugar beet industry would suffer "massive harm . . . and very likely lead to its demise in the Western Plains and Northwest where farmers on dependent on the technology for their livelihoods."

The request filed last Thursday in U.S. District Court in California said uprooting the stecklings would create an unavailability of seeds for sugar beets in 2012, resulting in $482 million in damages to the industry.

It also stated that it would destroy millions of dollars spent by the companies on research and development and hinder an effective appeal.

"We believe the court's action overlooked the factual evidence presented that no harm would be caused by these plantings," said David Snively, general counsel for Monsanto, in a written statement. "We intend to seek an immediate stay of this ruling and appeal to the Court of Appeals."

Monstanto is joined by American Crystal Sugar Company, Syngenta Seeds and Betaseed Inc., in seeking the stay.

Luther Markwart, executive vice president of the American Sugar Beet Growers Association, said the group was not a party in the lawsuit and that the potential impact on the sugar beet crop in 2012 wasn't yet known.

"But clearly, the bottom line is we disagree with what the court ruled," Markwart said.

Sugar beets are planted on more than 1 million acres in 10 states, with Minnesota, North Dakota and Idaho being the top producers.

The judge said the USDA failed to conduct the environmental review he demanded in his August ruling before issuing permits authorizing the planting of the seed plants.

The August ruling came after a challenge by the environmental groups to the Animal and Plant Health Inspection Services' deregulation of genetically modified sugar beets. The beets have been planted in the U.S. for four years.

The government sought a stay of White's decision, but he denied the request.

"We are now in discussion with the Department of Justice and we are exploring all options," said APHIS spokesman Andre Bell.

As part of White's ruling, a preliminary injunction against planting the seed plants will take effect Dec. 6.

George Kimbrell, an attorney for the Centers for Food Safety, one of the leading groups challenging the USDA's deregulation of genetically modified sugar beets, called White's ruling a "groundbreaking victory for farmers and the environment.

"This is the first time ever a federal court ordered an illegal biotech crop destroyed," he said.

Paul Atchitoff, of Earthjustice, a nonprofit environmental law firm that acted as lead counsel in the lawsuit, said White's ruling is "an indication that the government needs to start doing its job. The USDA needs to stop ignoring the environmental laws regarding genetically modified crops."

Atchitoff said APHIS' decision to issue permits to plant stecklings came less than a month after White ruled the beets could not be grown.

"The government's conduct is really outrageous," he said. "The court had just said in August the beets could not be grown and the government turned around and gave the industry the opportunity to grow them."

White's ruling followed the release by APHIS of a preliminary plan to let farmers plant genetically modified sugar beets until a lawsuit is resolved. The 365-page report suggested farmers be allowed to plant Roundup Ready sugar beets under a closely monitored permit process to prevent contamination of other crops. Monitoring by APHIS was one of three options outlined in the report and the one preferred by federal officials.

The USDA established a 30-day period for public comment on the plan, which ends Dec. 6, the same date when the injunction granted by the California judge takes effect.